[SimplifyCFG] Select the first instruction that we can handle in `passingValueIsAlwaysUndefined` (#98802)

Fixes #98799.

1 files changed, 24 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 3fa3c0f..8f717cb 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -7573,11 +7573,31 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
     return false;
 
   if (C->isNullValue() || isa<UndefValue>(C)) {
-    // Only look at the first use, avoid hurting compile time with long uselists
-    auto *Use = cast<Instruction>(*I->user_begin());
+    // Only look at the first use we can handle, avoid hurting compile time with
+    // long uselists
+    auto FindUse = llvm::find_if(I->users(), [](auto *U) {
+      auto *Use = cast<Instruction>(U);
+      // Change this list when we want to add new instructions.
+      switch (Use->getOpcode()) {
+      default:
+        return false;
+      case Instruction::GetElementPtr:
+      case Instruction::Ret:
+      case Instruction::BitCast:
+      case Instruction::Load:
+      case Instruction::Store:
+      case Instruction::Call:
+      case Instruction::CallBr:
+      case Instruction::Invoke:
+        return true;
+      }
+    });
+    if (FindUse == I->user_end())
+      return false;
+    auto *Use = cast<Instruction>(*FindUse);
     // Bail out if Use is not in the same BB as I or Use == I or Use comes
-    // before I in the block. The latter two can be the case if Use is a PHI
-    // node.
+    // before I in the block. The latter two can be the case if Use is a
+    // PHI node.
     if (Use->getParent() != I->getParent() || Use == I || Use->comesBefore(I))
       return false;